method for improved manufacturing of thick aluminium-copper rolled products

ABSTRACT

The invention relates to a method for manufacturing a product comprising an AlCu alloy comprising (weight per cent): Cu: 3.8-5.5 Mg: 0.2-0.8 Mn: 0.2-0.6 Ag 0.2-0.5 Si&lt;0.15 Fe&lt;0.20 Zn&lt;0.25 Cr&lt;0.05 Zr&lt;0.10, Ti&lt;0.15 others &lt;0.05, remainder aluminium. In an embodiment the method comprises naturally aging the product forming in at least one process, such as stretch forming, drawing, flow spinning, and/or bending and artificial aging at a temperature from 280 to 340° F. (138 to 171° C.) for a duration from 6 to 36 hours. The method is particularly useful to make armor products.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims priority from U.S. Patent Application Ser. No.61/419,050 filed Dec. 2, 2010 the contents of which is incorporatedherein by reference in its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates generally to aluminum-copper alloy products, andmore specifically such products optionally in the form of thick rolledproducts (ie with a thickness of a thickness of for example, from 0.5 to8 inches) intended to produce armored products.

2. Description of Related Art

Aluminum alloys have been widely used in light and medium armoredvehicles since the 1950s because of their superior ballisticperformance-weight balance combined with their good weldability, theirease of fabrication and their availability in a large range of productforms. With the recent conflicts, new threats appeared which madenecessary to significantly improve the ballistic resistance of anymaterials used for armor plates, including aluminum alloys, as well asto develop new materials with enhanced specific protection.

2139 has been identified as a promising alloy for high ballisticperformance, see for example, Lee W. M.—Dynamic MicrostructuralCharacterization of High Strength Aluminum Alloys—Masters Thesis—2008.

Products related to AA2139 are known for example from U.S. Pat. No.7,229,508.

For certain parts of armored vehicles, in particular the underbelly, theshape of the armoured plate can often be complicated and this maynecessitate employing a difficult shaping operation.

SUMMARY OF THE INVENTION

It was therefore a purpose of the present invention to provide a methodwhich enables forming thick Al—Cu wrought products suitable for armoredvehicles and even improve armored performance such as ballisticperformance and blast resistance of armored products, such as productsmade of AA2139.

An object of the invention was to provide a method for manufacturing aproduct comprising an AlCu alloy, said method comprising:

a) casting an ingot comprising (weight percent):

Cu: 3.8-5.5 Mg: 0.2-0.8 Mn: 0.2-0.6 Ag 0.2-0.5 Si<0.15 Fe<0.20 Zn<0.25Cr<0.05 Zr<0.10, Ti<0.15, optionally one or more of Hf, Sc and/or V,others <0.05, remainder aluminum,

b) optionally homogenizing the ingot at a temperature from 890 to 1010°F. (477 to 543° C.) for 2 to 48 hrs, and preferably at a temperaturefrom 950 to 990° F. (510 to 532° C.) for a duration of 12 to 36 hrs,

c) hot working the ingot to a product with a thickness from 0.5 to 8inches, preferably from 1 to 7 inches, and most preferably from 2 to 6inches,

d) solution treating the product from 930 to 1010° F. (499 to 543° C.),for a duration from 5 min to 10 hr,

e) rapidly cooling the product,

f) optionally cold working the product by cold rolling and/orstretching,

g) naturally aging the product,

wherein said method is optionally conducted in the order a-g.

A plate obtained by a method of the invention can advantageously undergoa forming operation to obtain a complicated shape and be artificiallyaged to obtain advantageous armor properties, such as ballisticproperties and blast resistance.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1. 20 mm FSP/0.3 cal AP performance balance for the tested alloys(the performance index is calculated as the relative difference betweenimpact velocity and residual velocity, a performance of 100% meansprojectile stopped.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT

Unless specified otherwise, all the indications relating to the chemicalcomposition of the alloys are expressed as a percentage by weight basedon the total weight of the alloy. The alloys are named in accordancewith the regulations of The Aluminum Association, known to those skilledin the art. The definitions of metallurgical tempers are given in theEuropean standard EN 515, and those are incorporated herein by referenceas if written.

Unless specified otherwise, the static mechanical properties, in otherwords the fracture strength R_(m), the yield strength at 0.2% elongationRp_(0.2) (“yield strength”) and the elongation at fracture A, aredetermined by means of a tensile test as per EN 10002-1, the samplingand direction of the test being defined by the standard EN 485-1 andthese are are also incorporated herein by reference in their entirety.

Unless specified otherwise, the definitions as per the standard EN 12258(incorporated herein by reference) apply.

According to the present invention, there is provided a method to make awrought product.

The method comprises successively casting an ingot comprising (weightpercent):Cu: 3.8-5.5 Mg: 0.2-0.8 Mn: 0.2-0.6 Ag 0.2-0.5 Si<0.15 Fe<0.20 Zn<0.25Cr<0.05 Zr<0.10, Ti<0.15, others <0.05, remainder aluminium. AA2139 isan example of the cast composition.Advantageously, the Ti content is from 0.02 to 0.13 wt. % and preferablyfrom 0.08 to 0.12 wt. %.Preferably, the Cu content is from 4.4 to 5.2 wt. %.The Mg content is preferably from 0.3 to 0.6 wt. %.Preferably the Mn content is from 0.3 to 0.5 wt. %.Advantageously, the alloy further includes at least one selected from Hf0.1-1.0 wt. %, Sc 0.03-0.6 wt. % and V 0.05-0.15 wt. %

Optionally the method comprises homogenizing the ingot at a temperaturefrom 890 to 1010° F. (477 to 543° C.) for 2 to 48 hrs, and preferably ata temperature from 950 to 990° F. (510 to 532° C.) for a duration of 12to 36 hrs.

The ingot is then hot worked to a product with a thickness from 0.5 to 8inches, preferably from 1 to 7 inches, and most preferably from 2 to 6inches. In a preferred embodiment the thickness of the product is from 1to 4 inch.

Hot working may be carried out by rolling, forging or extruding. In apreferred embodiment, hot working is carried out by rolling.

The product is then solution heat treated from 930 to 1010° F. (499 to543° C.), for a duration from 5 min to 10 hr and rapidly cooled.

Optionally the product is cold worked by cold rolling and/or stretching.

In an embodiment of the invention cold working is done solely by coldrolling from 0.5 to 10% and preferably from 1 to 5%. In another morepreferred embodiment of the invention cold working is done solely bystretching from 0.5 to 10% and preferably from 1 to 5%. In yet anotherembodiment of the invention cold working is done by a combination ofcold rolling from 0.5 to 5% and stretching from 0.5 to 5%.

Finally the product is naturally aged. The final temper obtained afternatural aging comprises advantageously T3, T351, T3511, T36, T38, T39 orF.

The product obtained after natural aging can advantageously be formed toa complicated shape.

Advantageously, the method of the invention further comprisessuccessively forming in at least one process, such as stretch forming,drawing, flow spinning, and/or bending, and artificial aging at atemperature from 280 to 340° F. (138 to 171° C.) for a duration from 6to 36 hours.

Artificial aging may be carried out in one or several steps. The finaltemper obtained after artificial aging may be referred to as T8, T83,T851, T8511, T86, T852, T87, or T89.

Products obtained by the method of the invention have after artificialaging an even improved armor performance compared to products of similarcomposition in a T8 temper which was obtained without the steps ofnatural aging and forming to a complicated shape.

Although they are not bound to a specific theory, the present inventorbelieve that the “dual cold working” of some embodiments of the methodof the invention: that is cold working before natural aging and formingafter natural natural aging contribute the high armor performance of theproducts of the invention.

An armor product comprising a product made by the method of theinvention is particularly advantageous.

EXAMPLES Example 1

The ballistic performance of a selection of aluminium alloys has beentested: 5083-H131, 6061-T6, 7020-T6, 7449-T6, and 2139-T8. Two types ofprojectiles were used: 0.3 cal AP and 20 mm FSP. Projectile velocitieswere selected to guarantee the full perforation of the plates forstandard alloys and the residual velocities were measured by X-Rayflashes behind the tested plates.

The ballistic performances of alloys were compared in terms of residualvelocity and number of projected fragments. The AP-FSP performancebalances of the tested materials are compared in FIG. 1. Post-mortemoptical and electronic sectional observations of the perforated plateswere performed and the failure mechanisms were classified as follows:

-   -   Low to medium strength alloys (5xxx and 6xxx) failed by ductile        hole growth. The residual velocities measured on these alloys        were quite high but only a few fragments were projected behind        the specimen.    -   High strength 7xxx alloys failed by discing (rear plate failure)        causing high spalling behind the armor plate and Adiabatic Shear        Band (ASB) initiation, propagation and finally shear cracking.    -   Alloy 2139 exhibited the better AP-FSP balance with a ductile        bulging failure mode.

Example 2

A slab made of AA2139 was cast, homogenized, hot rolled to 2.5 inchthick plate, solution heat treated, stretched 3% and naturally aged to aT351 temper.

The plate was then stretched formed and artificially aged to a T8temper.

Ballistic performance was excellent, even improved compared to a T8temper obtained without intermediate T351 temper and stretched forming.

1. A method for manufacturing a product comprising an AlCu alloy, saidmethod comprising: a) casting an ingot comprising (weight percent): Cu:3.8-5.5 Mg: 0.2-0.8 Mn: 0.2-0.6 Ag 0.2-0.5 Si<0.15 Fe<0.20 Zn<0.25Cr<0.05 Zr<0.10, Ti<0.15, others <0.05, remainder aluminum, b)optionally homogenizing the ingot at a temperature from 890 to 1010° F.for 2 to 48 hrs, for a duration of 12 to 36 hrs, c) hot working theingot to a product with a thickness from 0.5 to 8 inches, d) solutiontreating the product from 930 to 1010° F., for a duration from 5 min to10 hr, e) rapidly cooling the product, f) optionally cold working theproduct by cold rolling and/or stretching, g) naturally aging theproduct, wherein said method is optionally conducted in the order a-g.2. A method of claim 1, wherein a final temper of the product comprisesT3, T351 T3511, T36, T38, T39 or F.
 3. A method of claim 1, wherein saidcold working f) is done solely by cold rolling from 0.5 to 10%.
 4. Amethod of claim 1, wherein said cold working f) is done solely bystretching from 0.5 to 10%.
 5. A method of claim 1, wherein said coldworking f) is done by a combination of cold rolling from 0.5 to 5% andstretching from 0.5 to 5%.
 6. A method of claim 1, wherein the productis further transformed by i) forming comprising at least one processoptionally comprising stretch forming, drawing, flow spinning, and/orbending, j) artificial aging at a temperature from 280 to 340° F. for aduration from 6 to 36 hours.
 7. A method according to claim 6, wherein afinal temper after said artificial aging comprises T8, T83, T851, T8511,T86, T852, T87, or T89.
 8. A method of claim 6, wherein the Ti contentis from 0.02 to 0.13 wt. %.
 9. A method of claim 6, wherein Cu ispresent in an amount from 4.4 to 5.2 wt. %.
 10. A method of claim 6,wherein Mg is present in an amount from 0.3 to 0.6 wt. %.
 11. A methodof claim 6, wherein Mn is present in an amount from 0.3 to 0.5 wt. %.12. A method for manufacturing a product comprising an AlCu alloy, saidmethod comprising: a) casting an ingot comprising (weight percent): Cu:3.8-5.5 Mg: 0.2-0.8 Mn: 0.2-0.6 Ag 0.2-0.5 Si<0.15 Fe<0.20 Zn<0.25Cr<0.05 Zr<0.10, Ti<0.15, at least one selected from Hf 0.1-1.0 wt. %,Sc 0.03-0.6 wt. % and V 0.05-0.15 wt. %, others <0.05, remainderaluminum, b) optionally homogenizing the ingot at a temperature from 890to 1010° F. for 2 to 48 hrs, for a duration of 12 to 36 hrs, c) hotworking the ingot to a product with a thickness from 0.5 to 8 inches, d)solution treating the product from 930 to 1010° F., for a duration from5 min to 10 hr, e) rapidly cooling the product, f) optionally coldworking the product by cold rolling and/or stretching, g) naturallyaging the product, wherein said method is optionally conducted in theorder a-g, and wherein wherein the product is further transformed by i)forming comprising at least one process optionally comprising stretchforming, drawing, flow spinning, and/or bending, j) artificial aging ata temperature from 280 to 340° F. for a duration from 6 to 36 hours. 13.An aluminium alloy product obtained by a method of claim
 1. 14. Aproduct according to claim 13, wherein the product is a rolled product.15. A product according to claim 13, wherein the product is an extrudedproduct.
 16. A product according to claim 13, wherein the product is aforged product.
 17. An aluminium alloy product obtained by a method ofclaim
 6. 18. A product according to claim 17, wherein the product is arolled product.
 19. A product according to claim 17, wherein the productis an extruded product.
 20. A product according to claim 17, wherein theproduct is a forged product.
 21. An armour product comprising a productof any one of claim 17.